DNA Gyrase - DNA gyrase, the enzyme that is responsible for DNA supercoiling in prokaryotes, was discovered in this laboratory two years ago. The enzyme has now been purified to homogeneity from E. coli. As predicted from genetic studies, the enzyme is made up of two different subunits, the products of the genes for oxolinic acid resistance (na1A) and coumermycin resistance (cou). The DNA-relaxing activity of the enzyme is specifically inhibited by oxolinic acid, while the ATP hydrolysis coupled to the supercoiling reaction is inhibited by coumermycin. Thus the Cou subunit appears to be responsible for energy transduction, while the Nal subunit supplies the necessary nicking-closing function.